NCV7321

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5

FUNCTIONAL DESCRIPTION

Overall Functional Description

LIN is a serial communication protocol that efficiently

supports the control of mechatronic nodes in distributed

automotive applications. The domain is class−A multiplex

buses with a single master node and a set of slave nodes.

The NCV7321 contains the LIN transmitter, LIN receiver,

power−on−reset (POR) circuits and thermal shutdown

(TSD). The LIN transmitter is optimized for the maximum

specified transmission speed of 20 kB with EMC

performance due to reduced slew rate of the LIN output.

The junction temperature is monitored via a thermal

shutdown circuit that switches the LIN transmitter off when

temperature exceeds the TSD trigger level.

The NCV7321 has four operating states (unpowered

mode, standby mode, normal mode and sleep mode) that are

WAKE and activity on the LIN bus.

OPERATING STATES

Sleep Mode

Normal mode

Standby mode

Unpowered

Figure 3. State Diagram

LIN Wake−Up or Local Wake−Up

EN = High for t > T_enable

EN = High for t > T_enable

EN = Low for t > T_disable

− LIN Transceiver: OFF

− LIN Term: 30 k

W

− INH Pin = High

− RxD: Low After a Wake−up/

Floating Otherwise

− TxD: Wake−up Source Flag

− LIN Transceiver: OFF

− LIN Term: Floating

− INH Pin: Floating

− RxD: Floating

− TxD: Weak Pull−down

− LIN Transceiver: OFF

− LIN Term: Current Source

− INH Pin: Floating

− RxD: Floating

− TxD: Weak Pull−down

− LIN Transceiver: ON

− LIN Term: 30 k

W

− INH Pin: High

− RxD: Received LIN Data

− TxD: Weak Pull−down

Transmitter Input

Unpowered Mode

the chip is kept in a safe unpowered state. LIN transmitter is

inactive, both LIN and INH pins are left floating and only a

weak pull−down is connected on pin TxD. Pin RxD remains

floating.

The unpowered state will be entered from any other state

Standby Mode

Standby mode is a low−power mode, where LIN

transceiver remains inactive while INH pin is driven high to

activate an external voltage regulator – see Figure 2.

Depending on the transition which led to the standby mode,

pins RxD and TxD are configured differently during this

mode. A 30 k

W resistor in series with a reverse−protection

Standby mode is entered in one of the following ways:

power−on−reset level. In this case, RxD Pin remains

high−impedant and the pull−down applied on pin TxD

remains weak.

in the sleep mode. Pin RxD is pulled low while pin

TxD signals the type of wake−up leading to the standby

mode – its pull−up remains weak for LIN wake−up and

it is switched to strong pull−down for the case of local

wake−up (i.e. wake−up via Pin WAKE).

While in the standby mode, the configuration of Pins RxD

and TxD remains unchanged, regardless the activity on

WAKE and LIN Pins – i.e. if additional wake−ups occur

during the standby mode, they have no influence on the chip

configuration.

Normal Mode

In normal mode, the full functionality of the LIN

transceiver is available. Data according the state of TxD

input are sent to the LIN bus while pin RxD reflects the

logical symbol received on the LIN bus – high−impedant for

recessive and Low for dominant. A 30 k

W resistor in series